Methodology and Apparatus for Topology Discovery and Mapping of Chained Network Services

1. A method of mapping a chain of network service functions on a computer network, the method comprising: sending a request packet from a discovery source to a first service function of the chain of network service functions on the computer network; encapsulating the request packet with a network service header at the first service function, wherein the network service header comprises an identifier of the request packet as being an Operations, Administration and Maintenance (OAM) packet and an OAM payload; inserting metadata identifying the first service function into the OAM payload at the first service function; forwarding the request packet from the first service function to one or more subsequent service functions in the chain of network service functions and each of the one or more subsequent service functions inserts additional metadata identifying a respective one of the one or more subsequent service functions into the OAM payload, before the each of the one or more subsequent service functions forwards the request packet to another of the one or more subsequent service functions, until the request packet is received by an egress service function, wherein when forwarded by the one or more subsequent functions, the request comprises metadata comprising the metadata identifying the first service function and the additional metadata identifying each of the one or more subsequent service functions; returning the request packet from the egress service function to the discovery source; and mapping the chain of network service functions at the discovery source based on the combined metadata to form a topology of the computer network from the order of linkage of the chain of the network service functions.

2. The method of claim 1 , wherein the OAM payload further comprises an OAM function type, wherein the OAM function type comprises one of a process-and-forward type and a reply type.

3. The method of claim 1 , wherein OAM payload further comprises OAM function data comprising metadata related to one or more network service functions of the chain of network service functions that have been identified.

4. The method of claim 1 , further comprising setting a time-to-live (TTL) value in the network service header of the request packet.

5. The method of claim 1 , further comprising decrementing a TTL value in the network service header of the request packet.

6. The method of claim 1 , wherein the request packet further comprises an identifier of a service function type stored as a type-length-value (TLV) sequence.

7. The method of claim 1 , further comprising returning an error code packet to the discovery source if a request of the received request packet is not supported.

8. A method of verifying a service function on a computer network, the method comprising: encapsulating a request packet with a network service header at a discovery source, wherein the network service header comprises an identification of the request packet as being an Operations, Administration and Maintenance (OAM) packet and an OAM payload; sending the request packet from the discovery source to a first service function of a service function chain on the computer network, wherein the request packet comprises metadata identifying a service function type and the service function is verified by validating the service function's function; determining if a service function type of the first service function matches the service function type identified by the metadata at the first service function; responsive to the service function type of the first service function matching the service function type identified by the metadata, sending a response from the first service function to the discovery source indicating that the service function has been identified; and responsive to the service function type of the first service function not matching the service function type identified by the metadata, forwarding the request packet from the first service function to a second service function in the service function chain and adding additional metadata to the request packet at the second service function to form a combination of the metadata and the additional metadata in the request packet.

9. The method of claim 8 , further comprising setting a time-to-live (TTL) value of the request packet based on the number of service function hops through the service function chain required to reach a destination service function on the computer network.

10. The method of claim 8 , wherein the service function type is one of deep packet inspection, firewall, load balancer, and policy configuration.

11. The method of claim 8 , further comprising decrementing a TTL value at each service function said request packet hops through.

12. The method of claim 8 , wherein an identifier of the service function type is stored as a type-length-value (TLV) sequence.

13. The method of claim 8 , further comprising returning an error code to the discovery source if a request of the request packet is not supported by the first or second service function.

14. The method of claim 8 , wherein the network service header identifies a request type of the request packet.

15. An apparatus for mapping a topology of a service function chain on a computer network, comprising: a circuit determining the topology by forming an Operations, Administration and Maintenance (OAM) packet with a network service header, sending the OAM packet to a service function of a service function chain on the computer network, the service function chain comprising a plurality of service functions chained together on the computer network, wherein the last service function in the service function chain is an egress service function, and wherein each of the plurality of service functions: receive the OAM packet; add metadata identifying a function type of the service function to the OAM packet; return the OAM packet to the circuit in response to the service function being an egress service function; and forward the OAM packet to a next service function in the service function chain in response to the service function not being an egress service function, and adding additional metadata at the next service function identifying a function type of the next service function to the OAM packet; and the circuit mapping an order of the service function chain received from an ingress service function to the egress service function on the computer network based on the metadata and additional metadata accumulated and combined at each service function in the service function chain, the metadata and the additional metadata describing the identified function type of the service function and the next service function, in the OAM packet received from the egress service function to form the topology.

16. The apparatus of claim 15 , wherein the circuit sets a time-to-live (TTL) value in the network service header to 1.

17. The apparatus of claim 15 , wherein the plurality of service functions decrement a TTL value in the network service header.

18. The apparatus of claim 15 , wherein the plurality of service functions add the metadata to the OAM packet as a type-length-value (TLV) sequence.

19. The apparatus of claim 15 , wherein the plurality of service functions return an error code to the circuit in response to a request of the request packet not being supported by any service function.

20. The method of claim 8 , wherein the service function type is obtained by a verification list accessible by the discovery source.